In a variety of subterranean and wellbore environments, tools of all sorts are deployed for a multitude of critical applications. The tools, referred as downhole tools, may comprise subsurface safety valves, flow controllers, packers, gas lift valves, sliding sleeves as well as a great many other tools and accessories. Many of these tools have relatively complex mechanical designs in order to be controlled remotely from the surface; e.g. the rig floor via wirelines, hydraulic lines, or coil tubings.
FIG. 1 shows a conventional downhole tool controller system 10, which includes a controller 12 and a signal source 14. Signal source 14 is shown located at or near the surface, but may be placed in any convenient location in or around a well 16. In the embodiment shown, controller 12 is conveyed into well 16 by a tubing 18. The downhole portion of downhole tool controller system 10 may be conveyed by other means, such as a wireline or coiled tubing. A downhole tool 20 is shown in proximity to controller 12, but may be variously located in well 16.
Signal source 14 sends signals into well 16 for controller 12 to detect. Based on the signal received, controller 12 triggers the downhole tool 20 to perform a prescribed action. Signal source 14 may create signals as pressure sequences or in other forms, such as changes in the flow rates, weights, or stress/strain.
In the most common form, signal source 14 creates pressure signals to control the downhole tool 20 via the controller 12. When such hydraulic control is employed, the pressure pulse may be sent via dedicated hydraulic control lines. However, due to the restricted space of the wellbore, the number of control lines that can be run in a well is greatly limited.
Attempts have been made to increase the number of tools that each hydraulic control line can control by using multiplexers, electric/solenoid controlled valves or custom-designed hydraulic devices and tools that respond to sequences of pressure pulses. For example, U.S. Pat. No. 7,182,139 issued to Rayssiguier et al. discloses a method that uses predetermined pressure levels to independently actuate specific well tools such that the number of well tools independently controlled may be greater than the number of fluid control lines.
U.S. Pat. No. 7,171,309 issued to Goodman improves upon the reliability of such approaches by using autocorrelation of command sequences. In accordance with this method, repeat signals of a priori unknown or undefined shape can be correlated to themselves to reliably distinguish intentional changes from random fluctuations or other operations performed on the well.
While these methods are useful in providing sophisticated controls of downhole tools, it is desirable to have controls that do not rely on the limited number of control lines. Furthermore, in many situations, a downhole tool may only need to be actuated once and be left alone. In such situations, the control or actuation mechanism may be more conveniently imbedded in the tool itself.